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Abstract

In the present study, the 26-residue amphipathic α-helical peptide A12L/A20L (Ac-KWKSFLKTFKSLKKTVLHTLLKAISS-amide) with strong anticancer activity and specificity was used as the framework to study the effects of helicity of α-helical anticancer peptides on biological activities. Helicity was systematically modulated by introducing D-amino acids to replace the original L-amino acids on the non-polar face or the polar face of the helix. Peptide helicity was measured by circular dichroism spectroscopy and was demonstrated to correlate with peptide hydrophobicity and the number of D-amino acid substitutions. Biological studies showed that strong hemolytic activity of peptides generally correlated with high hydrophobicity and helicity. Lower helicity caused the decrease of anti-HeLa activity of peptides. By introducing D-amino acids to replace the original L-amino acids on the non-polar face or the polar face of the helix, we improved the therapeutic index of A12L/A20L against HeLa cells by 9-fold and 22-fold, respectively. These results show that the helicity of anticancer peptides plays a crucial role for biological activities. This specific rational approach of peptide design could be a powerful method to improve the specificity of anticancer peptides as promising therapeutics in clinical practices.
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